Liquid-vapor separator



June 21, 1966 MODRAK ETAL 3,256,865

LIQUID-VAPOR SEPARATOR Original Filed Aug. 1, 1961 FIG.1

L INVENTORS 2 Thomqs M Modrak Y Marvm A. Brahler ATTORNEY 24% F|G.3 Kg

United States Patent 3,256,865 LIQUID-VAPOR SEPARATOR Thomas M. Modrak,Alliance, and Marvin A. Brahler, Louisville, (lhio, assignors to TheBabcock & Wilcox Company, New York, N.Y., a corporation of New JerseyContinuation of application Ser. No. 128,519, Aug. 1,

1961. This application Jan. 24, 1964, Ser. No. 341,480

Claims. (Cl. 122-491) This application is a continuation of application,Serial No. 128,519, filed August 1, 1961, now abandoned.

This invention relates in general to a liquid-vapor separator, and moreparticularly to an improved steam and water separating drum of a steamgenerator.

Heretofore, the drums of industrial type steam generators with steamingcapacities of 14,000 to 60,000 pounds -of steam per hour have beengenerally provided with an internal bafile construction extending alongthe length of the drum for defining a compartment separated from thedrum water space for receiving the steam and water mixture generated inriser tubes. In units wherein it was desirable, for reasons of economyor otherwise, to effect primary separation of the steam and watermixture by gravity, the compartment was generally formed with aco-extensive unobstructed outlet through which the steam and watermixture collected in the compartment was discharged directly into thesteam space of the drum. In the steam space the heavy water particles ofthe mixture would be separated from the lighter steam particles bygravity as the steam particles would seek the steam outlet of the drum,the separated water being recirculated through the unit while theseparated steam was taken off and delivered to a point of use.

In units of this type experience shows that, for various reasons, thereis little likelihood that all of the riser tubes will deliver a mixtureof the same quality into the mixture receiving compartment of the drum.For this reason a maldistribution of flow was likely which could resultin operating difficulties, e.g., effecting undesirable water levelgradients and/or effecting localized overloading or underloading of thesecondary separating equipment, either of which could result inexcessive moisture carryover.

Therefore, an object of the invention is to provide an improvedarrangement whereby the distribution of the steam and water mixturereceived in the mixture receiving compartment of the steam and waterseparating drum is evened out and more uniformly distributed over thelength of the drum.

Another object is to provide an internal drum arrangement in which-thesteam and water mixture is discharged into the steam space of the drumat a relatively low velocity so as to enhance gravity separation thereofby increasing the amount of time available in which separation mayoccur.

Another object is to provide an improved drum internal constructionwhich significantly improves water level stability throughouttheoperating load range of the steam generating unit.

Still another object of the invention is to provide an improved druminternal construction wit-h the capacity to deliver satisfactory steampurity within the capacity range of a steam generating unit, and whichis relatively inexpensive, easily constructed and installed, and whichis positive in operation.

A feature resides in the provision that the improved drum internalconstruction of this invention minimizes carry-under, and thus enhancesthe delivery of solid water to the downcomer.

The various features of novelty which characterize our invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawing and descriptivematter in which we have illustrated and described a preferred embodimentof the invention.

In the drawings:

FIG. 1 is a front elevation view taken in section along the longitudinalaxis of a steam and water separating drum;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1; and

FIG. 3 is a sectional view taken along line 33 of FIG. 1.

Referring to the drawings, there is shown in FIG. 1 a cylindrical,elongated, horizontally disposed steam and water separating drum 10 ofthe type used in industrial and marine boilers. In the illustratedembodiment, the drum 10 is arranged to operate with a water level 11which defines the boundary between the lower water space 12 and theupper steam space 13. Several rows of high duty riser tubes 14 connectinto the drum 10 for discharging thereinto the steam and water mixture,and several rows of downcomer tubes 15 serve to carry water away fromthe drum 10 to effect the circulation of the unit.

Arranged internally of the drum 10 is a longitudinally extending baffie16 which is spaced from a circumferential wall portion of the drum anddefines therewith a compartment 17 for receiving the steam and watermixture discharged by the high duty riser tubes 14 which have theirrespective discharge end portions collected under baffle 16. As seen inFIG. 1, the ends of the bafile are spaced inwardly of the ends of thedrum 10, and end plates 18 close each of the ends of the compartment 17.The upper end 16A of the battle 16 extends to at least the water level11 of the drum 10. Thus it will be noted that the mixture receivingcompartment 17 is completely separated from the water space 12 of thedrum 10.

Disposed between the rows of downcomer tubes 15 and high duty risertubes 14, there may be provided other tubes 19 which function either aslower duty riser tubes or as downcomers depending upon the amount ofheat absorbed thereby.

According to this invention, a thin, substantially planar, perforatedbaflie or plate 20, having an open area of approximately 51%, isconnected to the upper end of the compartment baflle 16 alongsubstantially the entire length of the drum 10 to form an uprightextension, of the baffle. Preferably, the open area of the plate 20 isattained by numerous closely spaced small holes or perforations 21having a cumulative cross-sectional flow area sufficient to provide anevenly and widely dispersed slow moving outflow from the perforations 21to enhance gravity separation of water particles in the steam space 13wherein a significant portion of the vapor/liquid 3 separation takesplace. It has been found that if the perforations 21 in the plate 20 areA diameter holes on A" spacing, the open area will be suflicient toeffect the desired results.

The perforated bafile 20 is connected in overlapping spaced relationshipto the upper end 16A of the bafile 16 by means of suitable fasteners 22extended through spacer sleeves 23 at longitudinally spaced intervals.By this construction an opening or outlet 24 is defined between thebottom end 20A of the perforated plate 20 and the upper end 16A ofbaffle 16 at approximately the normal water level height. As shown, theperforated plate 20 is preferably angled inwardly of drum 10 so as toform an acute angle with respect to the water level. While notnecessarily restricted thereto, a 30 inclination from the vertical hasbeen found to give satisfactory results as will be herein described.

Extending between the upper end B of the perforated plate 20 and theadjacent wall portion of the drum 10 is a top plate which closes theupper end of the compartment 17. Thus, the steam and lower densityportions of the incoming steam-water mixture collected in thecompartment 17 are constrained to flow through the perforations 21 inthe baffle 20, in passing from the compartment 17 to the steam space 13of the drum 10, while the higher density portions of the incomingsteamwater mixture pass directly from the compartment 17 into the waterspace 12.

In operation, any maldistribution resulting from the discharge of anysteam and water mixtures of different qualities into the compartment 17is evened out behind the bafiles 16 and 20. This is effected for thereason that the varying qualities of the respective mixtures dischargedby each of the riser tubes are collected in a relatively large plenumwhich enables a remixing of the mixture to occur along with some naturalseparating taking place Within the compartment 17. This remixed mixtureis then evenly distributed over the length of the drum 10 by theperforated plate bafile 20. The separated steam and lighter mixturewithin compartment 17 flows out through the perforations 21 in the topportion of the bafl'le 20 as the heavier separated water flows outthrough the lower portions of the baffle 20 and slot 24, formed betweenbaffles 16 and 20.

Because the perforated plate 20 is angled downwardly, the steam-watermixture discharging therethrough leaves in a direction substantiallynormal to holes 21 and thus the mixture has imparted thereto a componentdirected downwardly toward the water level 11. Thus the fluid outflowfrom the perforations 21 in the baflle 20 is directed away from theentrance to the steam scrubbing apparatus 26 (or outlet from the steamspace 13) to effect a sweeping U-shaped path of flow whereby entrainedwater is separated from the fluid outflow by gravity within the steamspace 13.

While some steam carry-under may occur, it is confined near the surface11 of the drum water, and thus can be naturally separated by the steambubbling up through th water. Because the steam carry-under is near thesurface, there is little or a negligible amount of steam entrainment inthe downcomers 15. Consequently, the less steam entrained with the waterin the downcomers 15, the more circulation through the steam generatoris enhanced in a natural circulating unit.

The slot 24 formed between drum baffles 16 and perforated baffie 20 isespecially of advantage during low load circulation as it permits anywater separated upstream of the perforated plate 20 to be dischargeddirectly into the water space 12 of the drum 10 without going throughthe perforated plate 20. During boiler start-up, it is desirable to havethe least restriction possible on the riser circuits for holding thepressure drop to a minimum in order to permit some circulation throughthe boiler circuits which is necessary to prevent overheating of thetubes.

The slot 24 between baffles 16 and 20 and the large open area of baffle20 also minimizes the pressure drop through the drum internal baffleconstruction. Maintaining the pressure drop through the drum internalsas small as possible therefore enables either a reduction of the heightrequired for natural circulation, or a higher circulation rate for agiven capacity. Actual test in a p.s.i. installation has indicated thatthe pressure drop, over the capacity range of the unit, will not exceed.03 p.s.i. This has been found to be considerably less than the pressuredrop of other known internal bafile constructions.

A further advantage afforded by the use of a perforated baffle 20 asherein disclosed, is the small amount of drum water volume and end flowarea that is taken up by the described construction. Thus the larger theamount of water storage space available in a given drum, the smallerwill be the shrink and swell of the drum Water during swings in the loadto effect in a more stable or less fluctuating water level. Further,since the end flow area is not materially reduced by the perforatedbaffle construction of this invention, the water level gradient from oneend of the drum to the other will be maintained to a minimum. Actualtests have shown that water level fluctuation during steady loadoperation was only about /2 inch.

With the primary or main separation of the mixture discharged into thesteam space 13 is effected by gravity as described above, a steamscrubbing apparatus 26 may be arranged across the vapor outlet 31 of thedrum to further remove the final amounts of moisture carried by thesteam before leaving the drum 10. The scrubbing apparatus 26 preferablyis formed of closely spaced corrugated elements 27 constructed andarranged somewhat as disclosed in the patent to Fletcher 2,007,966. Thisscrubber device 26 removes the last particles of water carried by theseparated steam so that essentially dry steam is delivered to the steamoutlet 31. Included as part of the scrubber apparatus 26 is a suitabledrain 28. Completing the makeup of the drum are the usual safety valvenozzle connections 29.

In accordance with the invention, it will be noted that the entrance 30to the steam scrubber 26 is positioned at the furthest removed pointpossible from the perforated bafile 20. This is to provide the mixturedischarged into the steam space 13 with the greatest time and travelpossible in which to effect gravity separation in the steam space 13.

Thus it will be noted that while the perforated baflle 20 is not byitself a separating device; nevertheless, it provides an internal drumconstruction with. a capacity to deliver satisfactory steam puritywithin the capacity range of the boiler incorporating the same. Furtherthe perforated baflle construction in accordance with this inventionenhance-s circulation by minimizing carry-under, stabilizing waterlevel, and breaking localized concentration of steam and water mixturesto more evenly disgribute the steam and water mixture over the length ofthe rum.

While in accordance with the provisions of the statutes we haveillustrated and described herein the best form and mode of operation ofthe invention now known to us, those skilled in the art will understandthat changes may be made in the form of the apparatus disclosed with outdeparting from the spirit of the invention covered by our claims, andthat certain features of our invention may sometimes be used toadvantage without a corresponding use of other features.

What is claimed is:

1. In a natural circulation vapor generator, a cylindrical elongatedvapor-liquid separating drum having therein a liquid level defining theboundary between a liquid space and a vapor space, generating tubesopening into said drum for discharging a liquid-vapor mixture thereinto,and a partition longitudinally dividing said drum into a receivingchamber wherein said liquid-vapor mixture is discharged and a mainseparating chamber including a substantially unobstructed major portionof said vapor space wherein a significant portion of the vapor/liquidseparation takes place, said partition including a submerged baflieenclosing the discharge ends of said generating tubes, and an upwardlyextending substantially planar plate connected with said baflie andformed with perforations along its length and so arranged relative tothe remaining portions of said partition that the vapor and lowerdensity portions of the liquid-vapor mixture are constrained to flowthrough the perforations in passing from the receiving chamber directlyinto the main separating chamber, the perforations of said plate' havinga cumulative cross-sectional flow area sufiicient to provide an evenlydispersed slow moving fluid outflow from the perforations alongsubstantially the entire length of the drum to enhance gravityseparation of the liquid particles from said outflow within said mainseparating chamber, said partition being formed at approximately theheight of the liquid level with opening means through which liquidpasses directly from said receiving chamber to said liquid space, saidopening means extending substantially the entire length of thepartition' 2. In a natural circulation vapor generator, a cylindricalelongated vapor-liquid separating drum having therein aliquid leveldefining the boundary between a liquid space and a vapor space,generating tubes opening into said drum for discharging a liquid-vapormixture thereinto, a partition longitudinally dividing said drum into asubstantially unobstructed receiving chamber on one side of the drumwherein said liquid-vapor mixture is discharged and a main separatingchamber including a substantially unobstructed major portion of saidvapor space wherein a significant portion of the vapor/liquid separationtakes place, said partition including a substantially planar plateextending upwardly from said liquid level and being formed with auniform pattern of perforations along its length and means mounting saidplanar plate relative to the remaining portions of said partition sothat the vapor and lower density portions of the liquid-vapor mixtureare constrained to flow downwardly through the perforations toward saidliquid level in passing from the receiving chamber directly into themain separating chamber, the perforations of said plate having acumulative crosssectional flow area suflicient to provide an evenlydispersed slow moving outflow from the perforations along substantiallythe entire length of the drum to enhance gravity separation of theliquid particles from said outflow within the main separating chamber,and means defining a vapor outlet communicating with said mainseparating chamber and disposed near the top of and on the side of saiddrum opposite said receiving chamber, said outlet cooperating with saidplate to effect a sweeping U-shaped path of all of the vapor dischargedthrough the perforations in said plate whereby entrained liquid isseparated from the vapor within said main separating chamber.

3. In a natural circulation vapor generator, a cylindrical elongatedvapor-liquid separating drum having therein a liquid surface definingthe boundary between a liquid space and a vapor space, generating tubesopening into said drum for discharging a liquid-vapor mixture thereinto,a partition longitudinally dividing said drum into a receiving chamberinto which said liquid-vapor mixture is discharged and a main separatingchamber including a substantially unobstructed major portion of saidvapor space wherein a significant portion of the vapor/liquid separationtakes place, said partition including a submerged baffle enclosing thedischarge ends of said generating tubes, and an upwardly extendingsubstantially planar plate formed with perforations along its length andso arranged relative to the remaining portions of said partition thatthe vapor and lower density portions of the liquid-vapor mixture areconstrained to flow throughv the perforations in passing from thereceiving chamber directly into the main separating chamber, theperforations of said plate having a cumulative cross-sectional flow areasuflicient to provide an evenly dispersed slow moving outflow from theperforations to enhance gravity separation ofthe liquid particles fromsaid outflow within the main separating chamber, and means connectingsaid baffle and said plate in overlapping spaced relationship atapproximately the height of said liquid surface to form an openingimmediately adjacent said plate through which the liquid collected onthe upstream side of the plate passes directly from said plate to theliquid space.

4. In a natural circulation vapor generator, a cylindrical elongatedvapor-liquid separating drum having therein a liquid level defining theboundary between a liquid space and a vapor space, generating tubesopening into said drum for discharging a liquid-vapor mixture thereinto,a partition longitudinally dividing said drum into a receiving chamberon one side of the drum wherein said liquid-vapor mixture is dischargedand a main separating chamber including a substantially unobstructedmajor portion of said vapor space wherein a significant portion of thevapor/liquid separation takes place, said partition including anupwardly extending planar plate formed with a multiplicity of closelyspaced perforations along its length and so arranged relative to theremaining portions of said partition that the vapor and lower densityportions of the liquid-vapor mixture are constrained to flow downwardlythrough the perforations toward said liquid level in passing from thereceiving chamber directly into the main separating chamber, theperforations of said plate having a cumulative cross-sectional flow areasuflicient to provide an evenly and widely dispersed slow moving fluidoutflow from the perforations to enhance gravity separation of liquidparticles from said outflow within the main separating chamber, meansforming an opening in said partition immediately adjacent said platethrough which the liquid collected on the upstream side of the platepasses directly from said plate through said opening into said liquidspace, and means defining a vapor outlet communicating with the mainseparating chamber and disposed near the top of and on the side of thedrum opposite said receiving chamber, said outlet cooperating with saidplate to effect a sweeping U-shaped path of all of the outflow from theperforations in said plate, whereby entrained liquid is separated fromthe outflow within said main separating chamber.

5. In a natural circulation vapor generator, a cylindrical elongatedvapor-liquid separating drum having therein a liquid level defining theboundary between a liquid space and a vapor space, generating tubesopening into said drum for discharging a liquid-vapor mixture thereinto,a partition longitudinally dividing said drum into a receiving chamberon one side of the drum wherein said liquidvapor mixture is dischargedand a main separating chamber including a substantially unobstructedmajor portion of said vapor space wherein a significant portion of thevapor/liquid separation takes place, said partition including asubmerged baflie enclosing the discharge ends of said generating tubes,and an upwardly extending substantially planar plate inclined withrespect to the liquid level and formed with a multiplicity of closelyspaced perforations along its length and so arranged relative to theremaining portions of said partitionthat the vapor and lower densityportions of the liquid-vapor mixture are constrained to flow downwardlythrough the perforations toward said liquid level in passing from thereceiving chamber directly into the main separating chamber, theperforations of said plate having a cumulative cross sectional flow areasufiicient to provide an evenly and widely dispersed slow moving outflowfrom the perforations to enhance gravity separation of the liquidparticles from said outflow within the main separating chamber, saidplate having its lower edge projecting slightly below the liquid surfaceand being i'rrebverlapping spaced relationship with the submerged baffleat approximately the height of the liquid level to form a longitudinallyextending opening through which the higher density portions of theliquid-vapor mixture pass directly from the receiving chamber into theliquid space, and means defining a vapor outlet communicating with saidmain separating chamber and disposed near the top of and on the side ofsaid drum opposite said receiving chamber, said outlet cooperating withsaid plate to effect a sweeping U-shaped path of all of the outflow fromthe perforations in said plate whereby entrained liquid is separatedfrom the outflow within said main separating chamber.

References Cited by the Examiner UNITED STATES PATENTS KENNETH W.SPRAGUE, Primary Examiner.

JAMES W. WESTHAVER, Examiner.

1. IN A NATURAL CIRCULATION VAPOR GENERATOR, A CYLINDRICAL ELONGATEDVAPOR-LIQUID SEPARATING DRUM HAVING THEREIN A LIQUID LEVEL DEFINING THEBOUNDARY BETWEEN A LIQUID SPACE AND A VAPOR SPACE, GENERATING TUBESOPENING INTO SAID DRUM FOR DISCHARGING A LIQUID-VAPOR MIXTURE THEREINTO,AND A PARTITION LONGITUDINALLY DIVIDING SAID DRUM INTO A RECEIVINGCHAMBER WHEREIN SAID LIQUID-VAPOR MIXTURE IS DISCHARGED AND A MAINSEPARATING CHAMBER INCLUDING A SUBSTANTIALLY UNOBSTRUCTED MAJOR PORTIONOF SAID VAPOR SPACE WHEREIN A SIGNIFICANT PORTION OF THE VAPOR/LIQUIDSEPARATION TAKES PLACE, SAID PARTITION INCLUDING A SUBMERGED BAFFLEENCLOSING THE DISCHARGE ENDS OF SAID GENERATING TUBES, AND AN UPWARDLYEXTENDING SUBSTANTIALLY PLANAR PLATE CONNECTED WITH SAID BAFFLE ANDFORMED WITH PERFORATIONS ALONG ITS LENGTH AND SO ARRANGED RELATIVE TOTHE REMAINING PORTIONS OF SAID PARTITION THAT THE VAPOR AND LOWERDENSITY PORTIONS OF THE LIQUID-VAPOR MIXTURE ARE CONSTRAINED TO FLOWTHROUGH THE PERFORATIONS IN PASSING FROM THE RECEIVING CHAMBER DIRECTLYINTO THE MAIN SEPARATING CHAMBER, THE PERFORATIONS OF SAID PLATE HAVINGA CUMULATIVE CROSS-SECTIONAL FLOW AREA SUFFICIENT TO PROVIDE AN EVENLYDISPERSED SLOW MOVING FLUID OUTFLOW FROM THE PERFORATIONS ALONGSUBSTANTIALLY THE ENTIRE LENGTH OF THE DRUM TO ENHANCE GRAVITYSEPARATION OF THE LIQUID PARTICLES FROM SAID OUTFLOW WITHIN SAID MAINSEPARATING CHAMBER, SAID PARTITION BEING FROMED AT APPROXIMATELY THEHEIGHT OF THE LIQUID LEVEL WITH OPEING MEANS THROUGH WHICH LIQUID PASSESDIRECTLY FROM SAID RECEIVING CHAMBER TO SAID LIQUID SPACE, SAID OPENINGMEANS EXTENDING SUBSTANTIALLY THE ENTIRE LENGTH OF THE PARTITION.